Wafer pretreatment for copper electroplating

ABSTRACT

The present invention is directed to a pretreatment process for copper electroplating of via or trench features on a wafer, comprising filling the via or trench feature with a pretreatment solution, wherein the pretreatment solution comprises copper ions.

FIELD OF THE INVENTION

The present invention relates to a pretreatment process for copperelectroplating of via and trench features on a semiconductor wafer. Theprocess of the invention is particularly suited for plating deep vias(including through silicon vias (TSV)) or trenches, or those with highaspect ratios.

BACKGROUND OF THE INVENTION

Copper electroplating is one of the key processes for fabricatingsemiconductor interconnections. During copper electroplating, it issometimes difficult to achieve ideal fill results for vias, trenches andother connecting structures on a wafer.

In addition to the processes of chemical formulation and bathcomposition, the pretreatment process is of critical importance inachieving desired fill yield. The objective of pretreatment ispreventing air bubbles from remaining at the bottom of vias.

It is well understood that it is difficult to remove air from the bottomof a via using an electrolyte solution. U.S. Pat. No. 6,562,222 teachesthat acidic copper sulfate electrolytes can easily dissolve the copperseed layers due to the sulfuric acid contained in the electroplatingsolution. Thus, current industrial pretreatment practice is to soak thewafer in a surfactant solution or in deionized water prior to copperplating. For example, JP2008001963 discloses a pretreatment solutioncontaining ammonium and surfactants. U.S. Pat. No. 6,491,806 usesdeionized water in the wafer pretreatment, eliminating bubbles from thefill water in the vias. During electroplating, copper ions must diffusefrom the top of the via or trench to plate the bottom of the via ortrench. However, some copper will deposit on the top side wall of thevia or trench, due to a higher copper ion concentration near the sidewalls than at the bottom. This leads to pinching off, causing formationof voids or seams. Additives such as accelerators, suppressors andlevelers can inhibit the rate of top and top side wall deposit toachieve void free results. However, with vias of higher aspect ratios,the side wall constricts the copper ion channel, reducing diffusion ofcopper ions, and increasing the difficulty of preventing voids or seamsin the via or trench. Hence, a more robust solution is required.

US 2007/235343 A1 discloses the pretreatment with a solution comprisinga sulfur containing organic compound. Optionally also copper ions may bepresent in the pretreatment solution in a range of 0.01 to about 5.0g/l.

SUMMARY OF THE INVENTION

In view of the problems described, the present invention provides apretreatment process for copper electroplating of via and trenchfeatures on a wafer to reduce voids and defects, including filling thevia or trench feature with a pretreatment solution, wherein thepretreatment solution comprises copper ions from 10 g/L to 300 g/L.

The present invention also provides a process for copper plating, acopper electroplating pretreatment solution comprising copper ions andthe use of solutions comprising copper ions from 10 g/L to 300 g/L forpretreatment before copper electroplating.

DETAILED DESCRIPTION OF THE INVENTION

Due to the above-mentioned concerns and teachings in the prior art,copper electrolytes and copper ions had not previously been consideredfor use in pretreatment processes for plating vias or trenches.Surprisingly, however, it is found that using a pretreatment solutioncomprising copper ions in sufficient concentration can effectivelyeliminate the occurrence of voids or seams when plating copper in viasor trenches of a wafer. After the pretreatment step, the vias andtrenches are full of the pretreatment solution. During electroplating,the copper ions left at the bottom of a via compensate for limiteddiffusion of copper ions from the electroplating solution to the bottomof the via, and are immediately available as a copper source for platingon the surface of the bottom of the via. Thus, an ideal and desired fillresult can be more easily achieved, especially for vias or trenches ofgreater aspect ratio or depth.

Because of the copper ions left in vias or trenches, the presentinvention can reduce the time required for electroplating. Lessover-plating and enhanced uniformity can also be achieved. Commonstep-up current densities for plating are unnecessary and a highercurrent density can be used from the onset of the plating process.Additionally, a larger range in the quantity of additives in theelectroplating solution can be controlled during the electroplatingprocess without causing undesired results.

The copper electroplating pretreatment solution used in the process ofthe present invention contains 10 g/L to 300 g/L of copper ions,preferably, 10 g/L to 136 g/L of copper ions, more preferably, 20 g/L to200 g/L, even more preferably, 30 g/L to 136 g/L. And preferably, thepretreatment solution has a higher copper concentration than theelectrolyte used in a copper electroplating process. The electrolytecurrently used in a copper electroplating process typically containscopper ions from 30 g/L to 100 g/L.

Copper ions can be obtained by any source commonly used in thesemiconductor field, including but not limited to copper sulfate, copperalkanesulfonate, copper phosphate, copper fluoroborate, and coppercyanide or similar copper salts. Preferably, copper ions may be providedby copper sulfate or copper methanesulfonate.

Additives such as accelerators (brighteners), suppressors, and levelersare typically included in a copper electroplating solution to improveelectroplating behavior by improving surface deposition and thicknessuniformity and enhancing chemical reactions and filling of high aspectratio features.

Such additives can also be optionally added to the pretreatment solutionused in the process of the present invention.

Accelerators (or brighteners) are used for accelerating size reductionof deposited particles. The accelerator typically is sulfur-containingorganic compounds and relatively increases rate of copper deposition ina pattern on which a trench with a narrow width is formed. Examples ofsuitable accelerators are set forth in U.S. Pat. No. 6,679,983 includingn,n-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester;3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;3-mercaptopropylsulfonic acid (sodium salt); carbonicacid-dithio-o-ethylester-s-ester with 3-mercapto-l-propane sulfonic acid(potassium salt); bissulfopropyl disulfide;3-(benzthiazolyl-s-thio)propyl sulfonic acid (sodium salt); pyridiniumpropyl sulfobetaine; 1-sodium-3-mercaptopropane-1-sulfonate; disodiumbis-(3-sulfopropyl)disulfide; or mixtures thereof. Preferably, theaccelerator comprises disodium bis-(3-sulfopropyl)disulfide. Theconcentration of the accelerator in the pretreatment solution of thepresent invention is preferably from 0 mL/L to about 50 mL/L, morepreferably from 0 mL/L to 35 mL/L. The concentration of the activecompound of the accelerator in the pretreatment solution of the presentinvention is preferably from 0 ppm to 400 ppm.

Suppressors are used for increasing an over voltage for depositing aplating copper at more uniform electrodeposition. Suppressors for copperelectroplating are generally oxygen-containing high molecular weightcompounds. Suitable suppressors include, but are not limited to,carboxymethylcellulose, nonylphenolpolyglycol ether,octandiolbis-(polyalkylene glycolether), octanolpolyalkyleneglycolether, oleic acidpolyglycol ester, polyethylenepropylene glycol,polyethylene glycol, polyethylene glycoldimethylether, polyoxypropyleneglycol, polypropylene glycol, polyvinylalcohol, stearic acidpolyglycolester, polyethylene oxide, stearyl alcoholpolyglycol ether, and thelike. Preferably, the suppressor comprises poly(ethylene oxide-propyleneoxide). The concentration of the suppressor in the pretreatment solutionof the present invention is preferably from 0 mL/L to about 40 mL/L,more preferably from 0 mL/L to about 30 mL/L. The concentration of theactive compound of the suppressor in the pretreatment solution of thepresent invention is preferably from 0 ppm to 600 ppm.

Preferably, the pretreatment solution is essentially free of anyaccelerator, i.e. any sulfur-containing organic compound. “Essentiallyfree of any sulfur containing organic compound” means that the solutioncomprises less than 0.1 mg/L, preferably less than 0.01 mg/L, mostpreferably less than 0.001 mg/l of a sulfur containing organic compound.

Levelers are used for reducing surface roughness. They are similar tosuppressors in that they reduce deposition rate. Levelers for copperelectroplating generally comprise nitrogen-containing organic compounds.Compounds with an amino group or substituted amino groups are commonlyused. Such compounds are disclosed in U.S. Pat. No. 4,376,685, U.S. Pat.No. 4,555,315, and U.S. Pat. No. 3,770,598. Examples include1-(2-hydroxyethyl)-2-imidazolidinethione; 4-mercaptopyridine;2-mercaptothiazoline; ethylene thiourea; thiourea; alkylatedpolyalkyleneimine. Preferably, the leveler is1-(2-hydroxyethyl)-2-imidazolidinethione. The concentration of theleveler in the pretreatment solution of the present invention ispreferably from 0 mL/L to about 50 mL/L, more preferably from 0 to about40 mL/L. The concentration of the active compound of the leveler in thepretreatment solution of the present invention is from 0 ppm to 500 ppm.

The pretreatment solution of the present invention may also comprise asurfactant. The surfactant is used to lower the surface tension of thesolution. Useful surfactants include high molecular weight polymers,modified polyacrylic polymer, modified polysiloxane, preferablypolyglycol type polymers and co-polymers. The concentration ofsurfactant in the pretreatment solution may range from 0 wt% to 3 wt %.

The pretreatment solution of the present invention may also comprise anacid. The acid can be selected from the group consisting of sulfuricacid, alkanesulfonic acids (such as methanesulfonic acid, ethanesulfonicacid, propanesulfonic acid and trifluoro-methanesulfonmic acid),sulfamic acid; hydrochloric acid; hydrobromic acid; and fluoroboric acidand mixture thereof. Preferably, the acid is sulfuric acid,methanesulfonic acids or hydrochloric acid. The concentration of theacid is from 0 mL/L to about 40 mL/L.

According to one aspect of the present invention, the via or trenchfeature being plated has an aspect ratio greater than 2:1, preferably3:1 to 40:1. According to another aspect, the via or trench feature hasa depth of more than 10 micrometers, preferably 10 micrometers to 300micrometers.

According to a further aspect of the present invention, the process ofthe subject invention can further comprise a water rinse step or spindry step to remove the pretreatment solution from the surface of thewafer.

EXAMPLES AND COMPARATIVE EXAMPLES

Examples of the present invention and comparative examples will bedescribed. These examples illustrate only preferable embodiments of thepresent invention, and the present invention is not limited to theseexamples.

The examples show the pretreatment solutions, electroplating solutions,and via patterns. In each example, the test wafer was pretreated withthe pretreatment solution and then immersed in deionized water (DIwater) for about 2 seconds. The “pretreated” here means, for example,contacted, wetted or rinsed. For comparative examples 1 and 3, the stepof immersing in DI water was omitted because the pretreatment solutionsin both cases were ultra pure water. The wafer was then immersed in theelectroplating solution for plating. The anode was a copper anode.Except for Examples 15 and 16 and Comparative Examples 5 and 6, thepower supply supplied an average current density of 0.3 ASD (Ampere persquare decimeter). Plating was continued for about 40 minutes. ForExample 15 and Comparative Example 5 the power supply supplied anaverage current density of 0.1 ASD. Plating was continued for about 30minutes. For Example 16 and Comparative Examples 6 the power supplysupplied an average current density of 0.8 ASD. Plating was continuedfor about 30 minutes.

Comparative Example 1

Pretreatment solution: ultra pure water.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result showed voids in the bottom.

Example 1

Pretreatment solution: copper sulfate with copper ion concentration 10g/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 2

Pretreatment solution: copper sulfate with copper ion concentration 40g/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 3

Pretreatment Solution: copper sulfate with copper ion concentration 80g/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 4

Pretreatment solution: copper methanesulfonate with copper ionconcentration 90 g/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 5

Pretreatment Solution: copper methanesulfonate with copper ionconcentration 120 g/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 6

Pretreatment solution: copper methanesulfonate with copper ionconcentration 136 g/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Comparative Example 2

Pretreatment solution: CuPur™ T5000 (0.3% surfactant; available fromBASF).

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 10:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 60micrometers. The plating result showed voids in the bottom.

Comparative Example 3

Pretreatment solution: ultra pure water.

Electroplating solution: CuPur™ T 1010 (copper methanesulfonate, copperion concentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as anaccelerator available from BASF), CuPur™ T 3000 additive 6 mL/L (as asuppressor available from BASF), CuPur™ T 4000 additive 16 mL/L (as aleveler available from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result showed voids in the bottom.

Comparative Example 4

Pretreatment Solution: CuPur™ T5000 (0.3% surfactant; available fromBASF).

Electroplating solution: CuPur™ T 1010 (copper methanesulfonate, copperion concentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as anaccelerator available from BASF), CuPur™ T 3000 additive 6 mL/L (as asuppressor available from BASF), CuPur™ T 4000 additive 16 mL/L (as aleveler available from BASF).

The vias had an aspect ratio of 10:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 60micrometers. The plating result showed voids in the bottom.

Example 7

Pretreatment solution: copper sulfate with copper ion concentration 40g/L, sulfuric acid 10 g/L, and chloride ion 50 ppm.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 8

Pretreatment solution: copper sulfate with copper ion concentration 40g/L, CuPur™ T 2000 additive 15 mL/L (as an accelerator available fromBASF), CuPur™ T 3000 additive 5 mL/L (as a suppressor available fromBASF), CuPur™ T 4000 additive 5 mL/L (as a leveler available from BASF).

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 9

Pretreatment solution: copper methanesulfonate with copper ionconcentration 90 g/L, methanesulfonic acid 5 mL/L.

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 10

Pretreatment solution: copper methanesulfonate with copper ionconcentration 90 g/L, CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 2 mL/L (as a suppressoravailable from BASF).

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 8:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 50micrometers. The plating result was void-free and seam-free.

Example 11

Pretreatment solution: copper methanesulfonate with copper ionconcentration 90 g/L, CuPur™ T 2000 additive 12 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 2 mL/L (as a suppressoravailable from BASF), and surfactant (0.2 w%).

Electroplating solution: copper methanesulfonate (copper ionconcentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 6 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 16 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 10:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 60micrometers. The plating result was void-free and seam-free.

Example 12

Pretreatment solution: copper methanesulfonate with copper ionconcentration 120 g/L, CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 2 mL/L (as a suppressoravailable from BASF), and surfactant (0.2 w%).

Electroplating solution: CuPur™ T 1000 (copper sulfate, copper ionconcentration 40 g/L), CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 5 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 5 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 10:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 60micrometers. The plating result was void-free and seam-free.

Example 13

Pretreatment Solution: copper methanesulfonate with copper ionconcentration 120 g/L, CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 2 mL/L (as a suppressoravailable from BASF), and surfactant (0.2 w%).

Electroplating solution: copper methanesulfonate (copper ionconcentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 6 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 16 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 4:1 (depth:opening diameter), resultingfrom an opening having a diameter of 30 micrometers and a depth of 150micrometers. The plating result was void-free and seam-free.

Example 14

Pretreatment Solution: copper methanesulfonate with copper ionconcentration 180 g/L, CuPur™ T 2000 additive 15 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 2 mL/L (as an suppressoravailable from BASF), CuPur™ T 4000 additive 2 mL/L (as a leveleravailable from BASF), and surfactant (0.2 w %).

Electroplating solution: copper methanesulfonate (copper ionconcentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 6 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 16 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 10:1 (depth:opening diameter), resultingfrom an opening having a diameter of 6 micrometers and a depth of 60micrometers. The plating result was void-free and seam-free.

Comparative Example 5

Pretreatment Solution: copper sulfate with copper ion concentration 0.67g/L (10.6 mmol/L), CuPur™ T 2000 additive 1.06 g/L (3 mmol/L) (as anaccelerator available from BASF).

Electroplating solution: copper methanesulfonate (copper ionconcentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 6 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 16 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 6:1 (depth:opening diameter), resultingfrom an opening having a diameter of 10 micrometers and a depth of 60micrometers. The cross section of the features showed bottom voids.

Example 15

Pretreatment Solution: copper sulfate with copper ion concentration 60g/L.

Electroplating solution: copper methanesulfonate (copper ionconcentration 90 g/L), CuPur™ T 2000 additive 12 mL/L (as an acceleratoravailable from BASF), CuPur™ T 3000 additive 6 mL/L (as a suppressoravailable from BASF), CuPur™ T 4000 additive 16 mL/L (as a leveleravailable from BASF).

The vias had an aspect ratio of 6:1 (depth:opening diameter), resultingfrom an opening having a diameter of 10 micrometers and a depth of 60micrometers. The cross section of the features was void-free and seamfree.

Comparative Example 6

Pretreatment Solution: copper sulfate with copper ion concentration 0.67g/L (10.6 mmol/L), CuPur™ T 2000 additive 1.06 g/L (3 mmol/L) (as anaccelerator available from BASF).

Electroplating solution: copper sulfate (copper ion concentration 40g/L), CuPur™ T 2000 additive 15 mL/L (as an accelerator available fromBASF), CuPur™ T 3000 additive 5 mL/L (as a suppressor available fromBASF), CuPur™ T 4000 additive 10 mL/L (as a leveler available fromBASF).

Two trenches were tested. A 10 micrometer trench had an aspect ratio of11:2 (depth:width), resulting from a width of 10 micrometers and a depthof 55 micrometers. A 20 micrometer trench had an aspect ratio of 13:2(depth:width), resulting from a width of 20 micrometers and a depth of65 micrometers. The cross section of the features showed bottom defects.

Example 16

Pretreatment Solution: copper sulfate with copper ion concentration 60g/L.

Electroplating solution: copper sulfate (copper ion concentration 40g/L), CuPur™ T 2000 additive 15 mL/L (as an accelerator available fromBASF), CuPur™ T 3000 additive 5 mL/L (as a suppressor available fromBASF), CuPur™ T 4000 additive 10 mL/L (as a leveler available fromBASF).

Two trenches were tested. The 10 micrometer trench had an aspect ratioof 11:2 (depth:width), resulting from a width having 10 micrometers anda depth of 55 micrometers. The 20 micrometer trench had an aspect ratioof 13:2 (depth: width), resulting from a width having 20 micrometers anda depth of 65 micrometers. The cross section of the features wasdefect-free and seam-free.

The final filling features of the examples and comparative examples werechecked by cleavage cross-sectional optical microscope or scanningelectron microscope (SEM) and in some case by using focused ion beam(FIB) for double confirmation of the observation, and the results areshown in TABLE 1. The results show that the present invention has anexcellent effect in eliminating occurrence of voids and seams in thefilling result.

TABLE 1 No. Aspect ratio Filling result Comparative Example 1 8:1 Voidsoccurred Comparative Example 2 10:1  Voids occurred Comparative Example3 8:1 Voids occurred Comparative Example 4 10:1  Voids occurred Example1 8:1 Void-free and seam-free Example 2 8:1 Void-free and seam-freeExample 3 8:1 Void-free and seam-free Example 4 8:1 Void-free andseam-free Example 5 8:1 Void-free and seam-free Example 6 8:1 Void-freeand seam-free Example 7 8:1 Void-free and seam-free Example 8 8:1Void-free and seam-free Example 9 8:1 Void-free and seam-free Example 108:1 Void-free and seam-free Example 11 10:1  Void-free and seam-freeExample 12 10:1  Void-free and seam-free Example 13 4:1 Void-free andseam-free Example 14 10:1  Void-free and seam-free Comparative Example 56:1 Voids occurred Comparative Example 6 13:2  Defects occurred Example15 6:1 Void-free and seam-free Example 16 13:2  Defect-free andseam-free

Holding other parameters constant, Table 2 shows the filling results fordifferent concentrations of copper ions in the pretreatment solution.The results clearly show that a pretreatment solution of the presentinvention comprising any of the tested concentrations of copper ionswill eliminate occurrence of voids or seams. In Comparative Examples 5and 6 the same concentrations of copper ions and accelerator as used inExample 1 of US 2007/235343 were used. The experiments were repeated inexamples 15 and 16, respectively, however, without accelerator andhigher copper concentrations.

TABLE 2 [Cu²⁺] No. g/L Copper source Filling Result Comparative 1 0 —Voids occurred Comparative 5 0.67 Copper sulfate Voids occurredComparative 6 0.67 Copper sulfate Defects occurred Example 1 10 Coppersulfate Void-free and seam-free Example 2 40 Copper sulfate Void-freeand seam-free Example 3 80 Copper sulfate Void-free and seam-freeExample 4 90 Copper Void-free and seam-free methanesulfonate Example 5120 Copper Void-free and seam-free methanesulfonate Example 6 136 CopperVoid-free and seam-free methanesulfonate Example 15 90 Copper sulfateVoid-free and seam-free Example 16 40 Copper sulfate Defect-free andseam-free

The invention is not limited by the embodiments described above, whichare presented as examples only, and can be modified in various wayswithin the scope of protection defined by the appended patent claims.

1. A process for pretreating a via or trench feature on a wafer, theprocess comprising: filling a via or trench feature on a wafer with apretreatment solution comprising copper ions, wherein a concentration ofcopper in the pretreatment solution is in a range from 10 g/L to 300g/L, and the copper concentration of the pretreatment solution is higherthan a copper concentration of a copper electroplating solution. 2.(canceled)
 3. The process of claim 1, wherein the pretreatment solutionis essentially free of any sulfur-comprising organic compound.
 4. Theprocess of claim 3, wherein a concentration of the copper ions is in arange from 30 g/L to 136 g/L.
 5. The process of claim 1, wherein thepretreatment solution further comprises an additive.
 6. The process ofclaim 5, wherein the additive is at least one selected from the groupconsisting of an accelerator, a suppressor, a leveler, a surfactant, andan acid.
 7. The process of claim 6, wherein a concentration of theaccelerator in the pretreatment solution is in a range from 0 mL/L toabout 50 mL/L.
 8. The process of claim 6, wherein a concentration of anactive compound of the accelerator in the pretreatment solution is in arange from 0 ppm to 400 ppm.
 9. The process of claim 6, wherein aconcentration of the suppressor in the pretreatment solution is in arange from 0 mL/L to about 40 mL/L.
 10. The process of claim 6, whereina concentration of an active compound of the suppressor in thepretreatment solution is in a range from 0 ppm to 600 ppm.
 11. Theprocess of claim 6, wherein a concentration of the leveler in thepretreatment solution is in a range from 0 mL/L to about 50 mL/L. 12.The process of claim 6, wherein a concentration of an active compound ofthe leveler in the pretreatment solution is in a range from about 0 ppmto 500 ppm.
 13. The process of claim 6, wherein a concentration of thesurfactant in the pretreatment solution is in a range from 0 wt % toabout 3 wt %.
 14. (canceled)
 15. The process of claim 6, wherein theacid is selected from the group consisting of sulfuric acid,methanesulfonic acid, and hydrochloric acid.
 16. The process of claim 6,wherein a concentration of the acid in the pretreatment solution is from0 mL/L to about 40 mL/L.
 17. The process of claim 1, wherein the via ortrench feature has an aspect ratio greater than 2:1.
 18. The process ofclaim 1, wherein the via or trench feature has a depth of more than 10micrometers.
 19. The process of claim 1, further comprising: rinsing asurface of the wafer with water or spin drying the wafer, to remove thepretreatment solution from the surface of the wafer.
 20. A process forcopper electroplating a via or trench feature on a wafer, the processcomprising: contacting a via or trench feature on a wafer obtained bythe process of claim 1 with a copper electroplating solution; andapplying a current density to the wafer for a time sufficient to deposita copper layer onto the wafer.
 21. A copper electroplating pretreatmentsolution, comprising copper ions, wherein a concentration of copper inthe pretreatment solution is in a range from 10 g/L to 300 g/L.
 22. Aprocess for reducing electroplating voids and defects on a wafer, theprocess comprising: contacting a via or trench feature on a wafer with asolution comprising copper ions, wherein a concentration of the copperions in the solution is in a range from 10 g/L to 300 g/L, to obtain apretreated wafer; and then, copper electroplating the via or trenchfeature with a electroplating solution comprising copper, wherein thecopper concentration of the solution is higher than a copperconcentration of the electroplating solution.